The present invention generally relates to noise reduction circuits for video signals, and more particularly to a noise reduction circuit for a video signal capable of effectively eliminating a noise component appearing immediately after a rise in a luminance signal of a reproduced video signal.
Generally, a noise component is mixed within a video signal reproduced from a magnetic tape by a video signal magnetic recording and reproducing apparatus. However, especially the high-frequency component of the luminance signal in the video signal which is recorded and reproduced, is subjected to pre-emphasis, and the luminance signal is frequency modulated after the pre-emphasis is performed. Hence, the frequency of the frequency-modulated signal at parts immediately after a part (rise) where the level of the luminance signal rapidly changes from black level to white level, and immediately after a part (fall) where the level of the luminance signal rapidly changes from white level to black level, is particularly high because of the above preemphasis. Thus, in general, degradation is introduced in the signal-to-noise ratio of the recording and reproducing characteristic in the high-frequency range, in the magnetic recording and reproducing system. Therefore, the signal-to-noise ratio of the luminance signal at the above parts immediately after the rise and fall is poor, and it is highly desirable to positively eliminate the noise at these parts.
However, as will be described later in conjunction with the drawings, the conventional noise reduction circuit for eliminating the noise component in the reproduced luminance signal had a disadvantage in that the noise immediately after the rise in the reproduced luminance signal could not be eliminated effectively.